Those that are complete are easy to spot, especially with Google Earth's new navigation compass that makes directional rotations and angle views easier to manipulate. Even a monolith such as the Met Life building in New York City has enough details to make it identifiable even without its famous label.

Facades of glass, bricks and stone abound, but not everywhere. (Click here for cities where Google is working on models.)

Given the scope of the project (the whole world), it seems reasonable that Google would not yet be done rendering every single item for Google Earth 4 maps as rich 3D content. Rome wasn't built in a day, so why should its virtual counterpart be?

That is where the volunteer builders (slave laborers) come in. Google seems to be taking a cue from its recent acquisition, YouTube, which has flourished from user contributions. With the latest version of Google SketchUp, anyone can build rich 3D models to contribute to Google Earth.

Builders can sketch "on-site" through polygon drawing tools offered by Google SketchUp 6 right on top of existing Google Earth footprints. The finished and work-in-progress models can then be shared and stored as KML (Keyhole Markup Language) or KMX (the compressed version of KML) files at the Google 3D Warehouse.

Many Eiffel Towers, Chryslers Buildings, and Giza Pyramids can be found at the virtual warehouse. But if you want something really challenging to do this winter, there are no models of Gaudi's La Sagrada Familia church, the Taj Mahal or Easter Island heads to be found.